T Bar Spark Plug Socket 3/8″ Sq Drive 18mm A/F with Spring Clip Retention and Universal joint. Socket Suitable for Spark Plugs with an 18 mm Hexagon Conventional magnetic spark plug sockets can adversely affect hi-tech electronic control devices used on modern engines, but spring clip type is definitely safe with that point. Magnets easily break when dropped or struck hard, but not spring clip type. The broken pieces possibly stick to the engine, or get into inside the cylinder head. However the spring clip type avoids this problem. The clips are held in place by an internal brass guide which ensures perfect alignment of the spark plug into the threaded plug hole of the cylinder head, thus preventing thread damage. The brass guide eliminates stress loading and possible damage to the cerami.